TedEd: How does laser eye surgery work?

A TedEd by Dan Reinstein

 

In 1948, a Spanish ophthalmologist named José Ignacio Barraquer Moner decided to create an eye surgery that would eliminate external reliance. His procedure involved cutting off a patient's cornea and dunking it in liquid nitrogen. When it froze, he would use a miniature lathe to shape it, then sew it back onto the rest of the eye. The process was called keratomileusis, using the Greek words for carving and cornea. His surgery fixed what are called refractive errors. The cornea and lens work together to focus incoming light on the retina so that we can see. However, many small errors can unbalance this system. Myopia, or short-sightedness, occurs when the cornea focuses light just short of the retina. The opposite occurs with hyperopia, or far-sightedness. In Asigmatism, the cornea creates two different curves that focus the light in two different places. Even in people with normal eyes, the lens proteins grow as we age, causing presbyopia, or aging eyes. By our mid-40's, the lens starts having problems focusing, which are solved by glasses that refract light to the proper angle. Today, scientists use a far less invasive procedure involving excimer lasers to fix the corneas. The lasers accomplish the task by heating and evaporating parts of the cornea without hurting the eye. This is known as photoablation. To begin the process, doctors shave away a bit of the top of the cornea with a knife or lasers. Then, the laser can reshape the corneal bed to the proper shape. This usually takes less than 30 seconds per eye, after which the top is put back on and heals within hours. The name for this procedure is "laser in-situ keratomileusis", where in-situ stands for "on site". It is more commonly known as LASIK. This does come with risks, such as permanent blurriness, but this is extremely unlikely. There are also more accurate procedures called SMILE that use even smaller lasers. We can also cure aging eyes with this process. The doctors change one eye to be slightly far-sighted and the other eye to be near-sighted. The eyes adjust so that you can see from both distances.